Recycle of process condensate impurities in tigas

ABSTRACT

The present application relates to a plant and a hydrocarbon production process comprising the steps of (i) in a conversion step converting at least a feed stream thereby obtaining a conversion effluent stream comprising water, hydrocarbons such as raw gasoline, unreacted and/or partially reacted feed and/or inerts, (ii) In a separator separating the conversion effluent stream into at least a raw gasoline stream, a recycle stream and a process condensate stream comprising water and oxygenates, (iii) mixing the feed stream and the recycle stream upstream the conversion step, and (iv) adding at least part of the process condensate stream to the feed stream and/or the recycle stream and/or the mixed feed-recycle stream from step (iii).

The invention relates to an improved process and plant for the preparation of hydrocarbons useful as gasoline compounds from a feed comprising methanol.

Gasoline can be produced by conversion of raw methanol, pure methanol and/or dimethyl ether. In the process water is formed as a by-product. The water is separated (as process condensate) from the produced raw gasoline and recycle gas in a separator and send for water treatment as it comprises a number of impurities.

In a first aspect of the present invention is provided a process which provides an optimized output from the gasoline conversion.

In a second aspect of the present invention is provided a process which reduces the need for water treatment.

These and other advantages are achieved by a hydrocarbon production process comprising the steps of

-   -   In a conversion step converting at least a feed stream thereby         obtaining a conversion effluent comprising water, hydrocarbons,         unreacted, partially reacted feed and/or inerts,     -   In a separator separating the conversion effluent into at least         a recycle stream, raw gasoline and a process condensate stream         comprising water,     -   At one or more points mixing the feed stream and at least part         of the recycle upstream the conversion step, and     -   adding at least part of the process condensate stream to the         feed stream, recycle stream and/or mixed feed-recycle stream.

Various embodiments of the invention are disclosed and discussed in the following. These embodiments can either be employed each alone or in combination.

The conversion effluent may comprise various hydrocarbons such as raw gasoline, higher alcohols, aldehydes, ketones, ethers, olefins and/or aromatics.

By the present process and plant any convertible substances in the process condensate can be re-entered into the conversion loop whereby the output of the process may be increased compared to setups where the process condensate is simply sent to water treatment.

Also the present plant and process reduce the need for water treatment as the convertible substances in the water is reintroduced into the conversion step instead of being removed in downstream treatment of the condensate.

The feed to the process is preferably a methanol rich stream which also may comprise any of the following Dimethyl Ether (DME), higher alcohols, ketones, aldehydes, raw methanol, other alcohols, ethers and/or H2/CO mixtures.

The process condensate from the conversion process may comprise oxygenates of different types including alcohols, ketones, esters and/or aldehydes.

The oxygenates can be separated from the remaining process condensate which mainly consists of water. The separation of the oxygenates can for example be performed by distillation or stripping. The stream comprising the separated oxygenates is referred to as the recovered oxygenate stream. Preferably at least part of the process condensate added to the feed stream and/or the recycle stream and/or the mixed feed-recycle stream is a recovered oxygenate stream.

I.e. the at least part of the process condensate stream to the feed stream, recycle stream and/or mixed feed-recycle stream may be the recovered oxygenate stream.

The composition of the process condensate and the recovered oxygenate stream may depend on the conversion process, feed etc.

Some exemplary compositions and ranges for pressures and temperatures are given below. The values are based on a feed of raw methanol and a conversion process based on a ZSM-5 catalyst at T=250-475° C. and P=1-50 bar.

Process Condensate:

Temperature=75-105° C., preferably 90° C.

Pressure=2-8 barg, preferably 5.4 barg

Composition:

Compound wtppm Ethanol 50 wtppm Methanol 10000 wtppm Acetone 1100 wtppm 1-Propanol 200 wtppm Acetaldehyde 150 wtppm Methyl Ethyl Ketone 250 wtppm Water balance

Recovered Oxygenate Stream:

Temperature=75-105° C., preferably 90° C.

Pressure=15-40 barg, preferably 28 barg

Composition

Compound wtppm Ethanol 2800 wtppm Methanol 555000 wtppm Acetone 61100 wtppm 1-Propanol 11100 wtppm Acetaldehyde 8330 wtppm Methyl Ethyl Ketone 13880 wtppm Water balance

In most setups the conversion step is a methanol to gasoline (MTG) process in which the produced hydrocarbons comprises a mixture of various hydrocarbons boiling in the gasoline range, such as from C2 and higher e.g. up to C13, preferably C₅₊. Generally speaking in the conversion process the conversion of oxygenates in the feed stream is carried out in a converter in the presence of a catalyst being active known in the art in the reaction of oxygenates to higher hydrocarbons, preferably C₅₊ hydrocarbons.

In various setups more than one conversion reactor is used. In these setups the multiple converters may be arranged in parallel allowing recovery of one or more converter while one or more reactors are still in use.

The recovered oxygenate stream may be added to the feed stream and/or recycle and/or the stream of mixed feed/recycle in order to enter the conversion step thereby improving the output of the system compared to the case where the oxygenates are removed from the system together with the water etc. in the process condensate. I.e. the process provides an increased gasoline production because the unconverted oxygenates are recovered and recirculated back to the synthesis process instead of lost in the process condensate sent to water treatment. Furthermore the conversion of the recovered oxygenates reduce the need for treatment of the waste water as the oxygenates are utilized instead of being disposed of as part of the process condensate as known from existing processes.

FIG. 1 illustrates a process and plant 1 where feed 2 is mixed with recycle gas 3 and recovered oxygenate stream 4 is mixed into the feed/recycle gas stream at a mixing point 5.

Alternatively the recovered oxygenate stream is mixed into the recycle stream upstream the feed mix point 5 at a second mixing point 7. The mixing is preferable carried out by quenching the recovered oxygenate stream into the gas stream by means of a spray nozzle. Alternatively a static mixer can be used or the liquid and the gas can be mixed upstream of a heat exchanger.

Another alternative is to add the recovered oxygenate stream to the feed stream before the stream is evaporated or after the feed stream is evaporated as indicated by dotted lines 8 and 9. Another alternative is to spray/mix the liquid off-stream into the gas going to the reactor as indicated by dotted line 10.

The ketone, aldehydes and/or alcohols in the recovered oxygenate stream is together with the feed methanol converted to gasoline in the reactor 11. The effluent 12 is cooled/condensed in a series of heat exchangers 13 and the three phases are separated in the separator 14. The gas is recycled 15/purged 16 and the condensate 17 is sent to a distillation 18 for separation. The recovered oxygenate stream 4 from the separation comprises ketones, aldehydes and/or alcohols. 

1. A hydrocarbon production process comprising the steps of (i) in a conversion step converting at least a feed stream thereby obtaining a conversion effluent stream comprising water, hydrocarbons such as raw gasoline, unreacted and/or partially reacted feed and/or inerts, (ii) in a separator separating the conversion effluent stream into at least a raw gasoline stream, a recycle stream and a process condensate stream comprising water and oxygenates, (iii) mixing the feed stream and the recycle stream upstream the conversion step, and (iv) adding at least part of the process condensate stream to the feed stream and/or the recycle stream and/or the mixed feed-recycle stream from step (iii).
 2. A hydrocarbon production process according to claim 1 wherein the oxygenates are separated from the process condensate and added to the feed stream and/or the recycle stream and/or the mixed feed-recycle stream as a recovered oxygenate stream.
 3. A hydrocarbon production process according to claim 1, wherein the produced hydrocarbons comprise a mixture of hydrocarbons in the C2-C13 range, preferably comprising C5+.
 4. A hydrocarbon production process according to claim 1, wherein the feed comprises methanol, raw methanol, other alcohols, ketones, aldehydes, ethers and/or H₂/CO mixtures.
 5. A hydrocarbon production process according to claim 1, wherein the mixing of at least part of the process condensate comprising oxygenates into the feed stream, recycle stream and/or mixed feed-recycle stream is carried out by quenching the at least part of the process condensate into the feed stream and/or the recycle stream and/or the mixed feed-recycle stream by a spray nozzle.
 6. A hydrocarbon production process according to claim 1, wherein the process condensate is added to a stream upstream a heat exchanger.
 7. A plant comprising a converter, means for feeding a feed stream to the converter, a separator, means for returning at least part of a recycle stream from the separator to the converter, and means for mixing at least part of a process condensate from the separator into the means for feeding the feed stream and/or into the means for returning at least part of the recycle stream upstream the converter.
 8. A plant according to claim 7, comprising further means for separating oxygenates from the process condensate.
 9. A plant according to claim 8 wherein the means for separating oxygenates from the process condensate comprises a distillation unit and/or a stripper unit.
 10. Raw gasoline produced by the process according to claim
 1. 11. Raw gasoline produced by the plant according to claim
 7. 